yeah, i had a ladder slide back on me, then stop. mine caught a crack in the unscored cement. i'm lucky. as the ladder had already smashed the top panel of the window below. if it had gone back any further, then it would have put the big window beneath it through. and i would have gone through it as well....phew!
and luckily, the guy who lived there worked for the council, and he got the putty and glass for free. and he never asked for a penny off me! but i don't clean the top back window anymore. as his back yard is unscrored concrete. you would prolly slip up just walking about on it if it was wet